One more interesting property of neutron stars is the central energy density, as it is connected with the study of the time evolution of pulsars and the appearance of a possible phase transition. In Ref. [1]} a relation was found describing the upper bound for the density of cold baryonic matter, as
\(\frac{M}{M_{\odot }} = 4.25 \sqrt{\frac{10^{15}~{\rm gr}~{\rm cm^{-3}}}{\varepsilon _{\rm c}/c^{2}}}.\) 
